Control of variable-capacity pumps



June 14, 1960 G. T. SHOOSMITH 2,940,

CONTROL OF VARIABLE-CAPACITY PUMPS Filed Jan. 17, 1958 2 Sheets-Sheet 1.

"Inventor 9mm.

A ttomeys June 14, 1960 e. T. sHoosMrrH 2,940,429

CONTROL OF VARIABLE-CAPACITY PUMPS Filed Jan. 17, 1958 2 Sheets-Sheet 2 M Inventor A ttorn e 8 United States Patent CONTROL OF VARIABLE-CAPACITY PUlVIPS Guy Taite Shoosmith, St. Mary Bourne, England, assignor I to Plenty and Son Limited, Newbury, England Filed Jan. 17, 1958, Ser. No. 709,487

Claims priority, application Great Britain Jan. 21, 1957 Claims. (Cl. 121-41) This invention is concerned with the control of variable-capacity pumps, and is particularly drected to the problem of preventing overloading of a prime mover used to drive the pump.

In British specification No. 827,877, filed on December 4, 1956 there is described a variable-capacity pump of the sliding vane type which has a sliding block arranged to be moved by hydraulic liquid so as to vary the capacty of the pump. The flow of hydraulic liquid for this purpose is controlled by a valve which is actuated by a small pilot motor.

The present invention provides control apparatus by which a prime mover used for driving a pump of that construction can be protected against overloading, although the invention is applicable to pumps other than that described in British specification No. 827,877.

According to the invention, control apparatus for preventing overloading of a variable capacity pump having an hydraulically-movable sliding block comprises one or more limit switches arranged to stop and/or reverse a pilot motor controlling the hydraulic valve upon actuation of the switches by a switch-actuating device which, during operation of the pump, is connected to the delivery side thereof so as to be sensitive to variations in the delivery pressure.

If the delivery pressure builds up beyond a safe value, a part of the switch-actuating device is moved into contact with the switch or switches. Preferably, two switches are provided, one being actuated before the other so as to stop the pilot motor, while the other switch serves to reverse the'motor so that hydraulic liquid is supplied to move the sliding block in a direction which results in a reduction in the capacity of the pump. I

In order that the invention may be thoroughly understood, a specific pump having control apparatus in accordance with it will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a vertical section through the pump with certain parts omitted;

Figure 2 is an enlarged view of part of Figure 1; and

Figure 3 is a schematic diagram illustrating the switch mechanism.

The variable-capacity rotary pump shown in Figure 1 comprises a pump housing having a rotor shaft 12 provided with slots in which vanes 14 are arranged for limited sliding movement. The outer ends of the vanes 14 bear on flat surfaces formed on a rotor 16 which is rotatably located in a stationary sleeve 18 carried by a comparatively heavy sliding block 20. The inside of the housing 10 is so shaped that the sliding block 20 can move up and down so as to vary the eccentricity of the rotor 16 to the rotor shaft 12 and thus vary the capacity of the pump. Thus, spaces 22 and 24 are formed immediately above and below the upper and lower surfaces of the sliding block 20.

Movement of the sliding block 20 is efiected by supplying hydraulic liquid to the spaces 22 and 24 through pipes 26 and 28] The source of the hydraulic liquid is preferably the delivery side of the pump itself, so that in practice the liquid may be lubricating oil, fuel oil, kerosene or any other liquid which is capable of being handled by a rotary pump. The flow of hydraulic liquid is controlled by a piston valve 30 arranged on a part of the pump housing 10 directly above the sliding block 20, and liquid is supplied to the valve 30 through a pipe 32 and exhausted therefrom through pipes 34 and 36.

As shown in Figure 2, the valve 30 is connected by a mechanical linkage to the sliding block 20, so that when the sliding block reaches the desired position in the pump housing 10, the valve 30 is automatically stopped from delivering and withdrawing any more hydraulic liquid to and from the spaces 22 and 24 in the pump housing above and below the sliding block. The nature of the linkage can be widely varied, but in the arrangement shown in Figure 2 it consists of a lever 38 pivotally attached at its centre to the piston rod 40 of the piston valve 30. At one of its ends, the lever 38 has a pivotally-mounted nut 42 which is threaded on a lead screw 44, and at the other end it bears on a fulcrum 46 attached to the mid-point of another lever 48. For the sake of convenience, this second lever 48 will be termed the block follower lever because it is pivotally attached at one of its ends to a rod 50 extending up from the sliding block 20 and thus follows any movement of the block. The other end of the block follower lever 48 is pivotally secured to a stationary support 52.

When it is desired to move the sliding block 20 up or down into a new position so as to vary the capacity of the pump, the lead screw 44 is rotated in the appropriate sense by means of a small electric pilot motor 54 which is gearedjtoit, and the follower nut 42 is thereby moved along the lead screw. Such movement displaces the piston valve 30 which therefore supplies and withdraws hydraulic liquid to and from the spaces 22 and 24 on either side of the sliding block 20. This in turn causes the sliding, block and the rod 50 to move vertically, and the block follower lever 48 moveswith the block. Movement of the lever 48 alters the position of the fulcrum 46 for the other lever 38 in such a way that the centre ofthe lever 38 is restored to its original position, although the ends of the lever 38 are now in quite different postionsfrom those which they occupied originally.

The restoration of the centre of the lever 38 to its original, position results in the piston valve 30 similarly being restored to the position in which it cuts oil the supply or withdrawal of any further quantity of hydraulic liquid to and from the spaces 22 and 24 on either side of the sliding block 20. The sliding block is therefore hydraulically locked in its new position. Should the sliding block'move of its own accord from this position due to leakage of hydraulic liquid for example, the piston valve 30 will automatically open so as to allow hydraulic liquid to restore the sliding block to its correct position.

Electrical limit switches 56 and 58 are provided to limit the extent of the movement of the follower nut 42 along the lead screw 44 by cutting off the electrical supply to the pilot motor 54. However, it is still possible for the prime mover driving the pump to be overloaded should a blockage, for example, occur on the delivery side of the pump. To safeguard the prime mover, which can be an internal combustion engine or an electric motor, a pair of additional limit switches 60 and 62 are provided, these two switches being actuated by a switch-actuating device 64 which, during operation of the pump, is connected to the delivery side thereof so as to be sensitive to variations in the delivery pressure.

The switch-actuating device 64 comprises a small cylinder 66 and piston 68, one side of the piston being loaded by a compression spring 70, and the other side being A Mi i-k loaded in the' opposite direction by liquid bled into a compartment 71 the cylinder 66 through a pipe-' line shown partly at 72 from the delivery side of the pump, The piston 68 has a piston rod 74 extending through a seal at one end of the: cylinder. 66, and; the rod 74 is pivotallyrconnected byalink 76 to aacam-lever 78 pivotally mountedat one end 80 one stationary sup-' port (not shown). The free end of thecam-lever 78 has an arcuate cam surface 82 which can be brought into is and out of engagement with the pair of limit switches 60 and 62, movement of the lever 78 being efiected by variations in the pressure of the liquid acting on the piston68. V

. 7 During normal operation ofthepump, thecapacity of the pump is varied at will by closing the capacity increasa ing switch 84 (see Figure 3) or closingthe capacity- I decreasing switch 86, both switches being connected to the reversing starter 88 for the pilot motor 54. The

' spring 70 in the cylinder 66 of the switch-actuating device "64 presses the piston 68 against the pressure of the bled liquid'into a positionwhere the. piston rod'74 moves the cam-lever 78 out of contact with the limit switches 60 motor'54' and serves to prevent hydraulic liquid being supplied to move the; sliding block 20 in a direction which would increase the capacity. of the pump.

Continued'increase in the delivery pressure 'of the pump causes the cam-lever 78'to be moved still further into a a position where it closes the other limit switch 60 which -isnormally open. The switch 60 causes the pilot motor 54 to be'started up again, but this time in the reverse direction so that hydraulic fluid is'supplied to movethe sliding block 20 in a direction which results in the side willalso decrease, ande'ventually the cam-lever 78 (wand '62 by the switch-actuating device '64. 7

As already mentioned, the control apparatus'in' accordwillbe moved out of contact with the two limit switches a capacity of the pump being decreased. As the pump capacity decreases, the pressure build-up on its delivery ance with the present invention can housed on pumps other than that described in British specification No.

' 827,877, but when used on apump constructedas devalve designed to regulate the flow of hydraulic control fluid to and from a pump, a reversible electric pilot motor mechanically connected to said hydraulic valve whereby the position of said hydraulic. valve may be varied, at least one limit switch, electrical conduit means connecting said limit switch and said pilot motor together whereby said limit switch can at least stop said pilot motor, a switch-actuating 'device located adjacent said limit switch, movable means; forming part of 'said switchactuating device arranged to'actuate said'limit switch, a compartment within said switch-actuating device, an aperture leading from saidcompartment for connection to a sourceof variable-pressure fluid, said compartment being partially bounded by a portion of, said movable means whereby the pressure of said'variable-pressure fluid can move said movable means. I

2. Pump control apparatus as claimed :in claim'l having a 'first limit switch' and a second limit switch, electrical conduit means connecting said first limit switch and said pilot motor together whereby said first limit switch can stop's aid pilot motor, electrical conduit means connecting said second limit switchand said pilot motor whereby said second limit switch can reverse said pilot motor, said movable means of said. switch-actuating device being arranged to actuate said first limit switch before actuating said second limit switch. i

3. Pump control apparatus as claimed in claim 1 wherein said switch-actuating device includes a cylinder and a piston movable therein, said piston having one side loaded by a spring, said piston having an opposite side to said first side forming a boundary wall of said compartment in said switch-actuating device- 4. Pump control apparatus as claimed in claim 1, wherein said switch-actuating device includes a cylinder and a piston movable therein, a piston rodon said piston, a cam arranged to actuate said limit. switch, said cam beingmechanically' connected to said piston rod.: 5. Pump control apparatus as claimed in claim 1 wherein said switch-actuating device includes a cylinder and a piston movable therein, a pistonrod on. said piston,

"a lever pivotally mounted at one, endon a. stationary support, a pivotal connection between" said :lever and said piston rod, an arcuate cam surface on the free end of 'said lever, said arcuate cam surface being movable into and out of engagement with said limit switch; i

References Cited in the file of this fp'atent '.UNITED STATES PATENTS;

1,821,502 Ellis 2,12 7 ,265 Martin" 'Aug. 16, 1938 {2,214,552 Ferris Sept. 10, 1940 2,219,896 Harrington et a1 Oct. 29., 1940 "2,238,063 Kendrick Apr. 15, 1941 2,500,797 a Bullard Mar. 14, 1950 2,524,055 Hubert Oct. 3, 1950 2,588,522 Harris Mar. 11, 1952 2,621,632 Ifield Dec. 16,1952

Tucker s Aug. 11, 1 953 

